Cleared up to Tadak 80

You need to play slowly and with the long game in mind. The heroes are Construction, Berserker, Medic, Dark Priest, Guardian. You should use Kim Rocket and Kiket. You need to level them all to at least level 6 to push through. If you level up Dark to 6 first, you can charm the bounty enemies and defeat them all at once, making it easier to gather gas and resources. Other heroes will also become useful later on. Ultimately, you need to max out Fire level and use Kiket for random missile drops, while surviving with Guardian's shield twice (level 9). That's the only way to clear it.